RESEARCH SUMMARY 



In early September 1975, two clearcuts (14 and 17 acres; 5.7 and 

 6.9 ha), two sets of 4 small clearcuts (<1.5 acres; 0.6 ha each), and 

 one shelterwood cutting (22 acres; 8.9 ha) were broadcast burned 

 principally for seedbed preparation and fuel reduction on the Coram 

 Experimental Forest. The objective was to develop a model for pre- 

 dicting duff reduction (amount and percent) and mineral soil exposure 

 (percent) resulting from the fires, using only preburn measurements 

 for inputs. In addition, the influence of the fires on soil heating, soil 

 water content, and nonconiferous root mortality was quantified. 



Because of the relatively low maximum air temperatures and high 

 precipitation on the study area during August, the fuels were relatively 

 moist at the time of ignition. As a result, the fires generally spread 

 poorly, especially in the shelterwood, except where the fuels were 

 concentrated. The prescribed fires reduced the duff an average of 

 27 percent in the clearcuts and 11 percent in the shelterwood. Mineral 

 soil exposure averaged 19 percent in the clearcuts and 10 percent in 

 the shelterwood. The amount of water within the upper 4 inches (10. 2 

 cm) of soil was not changed greatly, there was no significant heating 

 of the surface soil above 113°F (45"" C), and root mortality was low. 



Multivariate regression analysis was used to derive prediction 

 equations for duff reduction and mineral soil exposure. However, 

 because of extremely poor correlation between the dependent variables, 

 duff reduction and mineral soil exposure, and all combinations of the 

 independent variables, no statistically valid equations resulted. The 

 expected correlation between duff consumption and lower duff water 

 content was not evidenced. This was attributed to the high water 

 content of the duff itself, which averaged nearly 150 percent in the 

 three blocks studied. These results substantiate Shearer's (1975) 

 conclusions. Broadcast burning for seedbed preparation should not 

 be attempted in this forest type when lower duff water contents exceed 

 about 100 percent. 



